1. Field of the Invention
This invention relates to alarm devices for use in interconnected alarm systems and, more particularly, to alarm devices and systems in which an adverse condition such as smoke sensed by one or more of the devices causes all of the interconnected devices to signal an alarm.
2. Description of Prior Art
Alarm devices such as smoke or intrusion alarm devices are often used to signal the existence of an adverse condition. Such devices are typically self-contained in that the sensing apparatus and the alarm apparatus are combined in a single unit which may be placed wherever required to protect the premises. In the case of smoke detection, it is common to locate a number of smoke alarm devices throughout the premises. For example, in a typical home installation, one unit may be placed in the bedroom area while other units may be located in the living area, the garage, and the basement. If the units are totally self-contained, only the unit sensing an adverse condition will signal an alarm. This is undesirable under certain conditions in that the alarm signalling the alarm may be located where it cannot be seen or heard, e.g., people sleeping in the bedroom area may not be awakened by a horn alarm sounding in the basement area. To overcome this problem, it has been suggested in the past that alarm devices be provided with remote alarms, thereby substantially extending the warning range of the detection equipment. In this respect, a smoke alarm located in a basement area may be provided with an auxiliary alarm in a bedroom area. While this certainly extends the warning range of the detection equipment, it has a disadvantage of adding significantly to the cost of the overall system since it requires multiple alarm devices for detection in a single location. Furthermore, the resulting system is totally disabled in the event that the power supply to the primary unit is disrupted for some reason.
The cost problem can be largely overcome by connecting the individual alarm units in parallel such that an adverse condition sensed by any one of the alarm devices will produce a warning signal on all of the interconnected units that are individually connected to operative sources of electric power. In such systems, however, an alarm device not connected to an operative source of electric power will neither sense for the presence of an adverse condition nor signal an alarm in response to the sensing of an adverse condition by another of the interconnected units. If, for example, in a home installation of a smoke detection system, a detector in a basement detects smoke, an interconnected detector located in the bedroom area will sound an alarm only if the bedroom unit is connected to an operative source of electric power. Similarly, the bedroom unit under such circumstances will not sense for smoke.